Glass composition for producing high strength and high modulus fibers

ABSTRACT

A glass composition including SiO 2  in an amount from 60.0 to 73.01% by weight, Al 2 O 3  in an amount from about 13.0 to about 26.0% by weight, MgO in an amount from about 5.0 to about 12.75% by weight, CaO in an amount from about 3.25 to about 4.0% by weight, Li 2 O in an amount from about 3.25 to about 4.0% by weight, and Na 2 O in an amount from 0.0 to about 0.75% by weight is provided. Glass fibers formed from the inventive composition may be used in applications that require high strength, high stiffness, and low weight. Such applications include, but are not limited to, woven fabrics for use in forming wind blades, armor plating, and aerospace structures.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority and all other benefits of U.S.Provisional Application Ser. No. 61/360,138 which is hereby incorporatedby reference in its entirety.

TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY

The present invention relates generally to a glass composition, and moreparticularly, to a high performance glass composition that possessesacceptable forming properties and whose components are melted in arefractory melter. Glass fibers formed from the inventive compositionpossess high strength and improved modulus and may be used to reinforcecomposite matrices where high strength and light weight are desired.

BACKGROUND

Glass fibers are manufactured from various raw materials combined inspecific proportions to yield a desired chemical composition. Thiscollection of materials is commonly termed a “glass batch.” To formglass fibers, typically the glass batch is melted in a melter or meltingapparatus, the molten glass is drawn into filaments through a bushing ororifice plate, and a sizing composition containing lubricants, couplingagents, and film-forming binder resins is applied to the filaments.After the sizing is applied, the fibers may be gathered into one or morestrands and wound into a package or, alternatively, the fibers may bechopped while wet and collected. The collected chopped strands may thenbe dried and cured to form dry chopped fibers or they can be packaged intheir wet condition as wet chopped fibers.

The composition of the glass batch and the glass manufactured from itare typically expressed in terms of percentages of the components, whichare mainly expressed as oxides. SiO₂, Al₂O₃, CaO, MgO, B₂O₃, Na₂O, K₂O,Fe₂O₃, and minor amounts of other compounds such as TiO₂, Li₂O, BaO,SrO, ZnO, ZrO₂, P₂O₅, fluorine, and SO₃ are common components of a glassbatch. Numerous types of glasses may be produced from varying theamounts of these oxides, or eliminating some of the oxides in the glassbatch. Examples of such glasses that may be produced include R-glass,E-glass, S-glass, A-glass, C-glass, and ECR-glass. The glass compositioncontrols the forming and product properties of the glass. Othercharacteristics of glass compositions include the raw material cost andenvironmental impact.

There is a unique combination of forming properties that permits a glassto be melted and distributed in a conventional refractory tank and glassdistribution system. First, the temperature at which the glass is heldmust be low enough so that it does not aggressively attack therefractory. An attack on a refractory can take place, for example, byexceeding the maximum use temperature of the refractory or by increasingthe rate at which the glass corrodes and erodes the refractory to anunacceptably high level. Refractory corrosion rate is strongly increasedas the glass becomes more fluid by a decrease in the glass viscosity.Therefore, in order for a glass to be melted in a refractory tank, thetemperature of the refractory must be kept below a certain temperatureand the glass viscosity (e.g., resistance to flow) must be maintainedabove a certain value. Also, the temperature of the glass in the meltingunit, as well as throughout the entire distribution and fiberizingprocess, must be high enough to prevent crystallization of the glass(i.e., it must be kept at a temperature above the liquidus temperature).

At the fiberizer, it is common to require a minimum temperaturedifferential between the temperature selected for fiberizing (i.e.,forming temperature) and the liquidus temperature of the glass. Thistemperature differential, ΔT, is a measurement of how easily continuousfibers can be formed without production of the fibers being interruptedby breaks caused from devitrification crystals. Accordingly, it isdesirable to have as large a ΔT as possible to achieve continuous anduninterrupted glass fiber formation.

In the quest for glass fibers having a higher end performance, ΔT has,at times, been sacrificed to achieve desired end properties. Theconsequence of this sacrifice is a requirement that the glass be meltedin a platinum or platinum-alloy lined furnace, either because thetemperature exceeded the maximum end use temperature of the conventionalrefractory materials or because the viscosity of the glass was such thatthe temperature of the glass body could not be held above the liquidustemperature while producing a glass viscosity high enough to keep therefractory corrosion at an acceptable level. S2-glass is one examplewhere both of these phenomena take place. The melting temperature ofS2-glass is too high for common refractory materials and the ΔT is verysmall (or negative), thus causing the glass to be very fluid and verycorrosive to conventional refractories at glass temperatures above theliquidus temperature. Conventional R-glass also has a very small ΔT, andis therefore melted in platinum or platinum-alloy lined melters.

Thus, there is a need in the art for high-performance glass compositionsthat retain favorable mechanical and physical properties (e.g., specificmodulus and tensile strength) and forming properties (e.g., liquidustemperature and forming temperature) where the forming temperature issufficiently low and the difference between the forming and liquidustemperatures is large enough to enable the components of the glasscomposition to be melted in a conventional refractory tank.

SUMMARY

In one embodiment of the invention, a composition that includes SiO₂ inan amount from about 60.0 to about 73.01% by weight, Al₂O₃ in an amountfrom about 13.0 to about 26.0% by weight, CaO in an amount from 0.0 toabout 4.0% by weight, MgO in an amount from about 5.0 to about 12.75% byweight, Li₂O in an amount from about 3.25 to about 4.0% by weight, andNa₂O in an amount from 0.0 to about 0.75% by weight is provided. Thephrase “% by weight”, as used herein, is intended to be defined as thepercent by weight of the total composition. Additionally, thecomposition may optionally contain trace quantities of other componentsor impurities that are not intentionally added. In exemplaryembodiments, the glass composition is free or substantially free of B₂O₃and fluorine, although either can be added in small amounts to adjustthe fiberizing and finished glass properties and will not adverselyimpact the properties if maintained below several percent. As usedherein, substantially free of B₂O₃ and fluorine means that the sum ofthe amounts of B₂O₃ and fluorine present in the composition is less than1% by weight of the composition. The sum of the amounts of B₂O₃ andfluorine present in the composition can be less than 0.5% by weight ofthe composition, or less than 0.2% by weight of the composition.Further, the glass composition possesses a forming temperature (alsoreferred to herein as the fiberizing temperature or the log 3temperature) that is low enough to utilize low cost refractory meltersinstead of conventional high cost platinum-alloy lined melters in theformation of the glass fibers.

In another embodiment of the present invention, a continuous glass fiberformed of the composition described above is produced using a refractorytank melter. By utilizing a refractory tank formed of refractory blocks,manufacturing costs associated with the production of glass fibersproduced by the inventive composition may be reduced. The glasscompositions may be used to form continuous glass strands for use inapplications where high strength, stiffness, and low density arerequired.

In yet another embodiment of the present invention, a reinforcedcomposite formed of a product a matrix material and a plurality offibers formed with the composition described above is provided. Thematrix material may be any suitable thermoplastic or thermoset resinknown to those of skill in the art, and include thermoplastics such aspolyesters, polypropylene, polyimide, polyethylene terephtalate, andpolybutylene, and thermoset resins such as epoxy resins, unsaturatedpolyesters, phenolics, vinylesters, and elastomers. The polymer resinscan be used alone or in combination to form the final composite product.

In a further embodiment of the present invention, a method of forming ahigh performance glass fiber is provided. The fibers may be formed byobtaining the raw ingredients and mixing the components in theappropriate quantities to give the desired weight percentages of thefinal composition. The mixed batch is then melted in a traditionalrefractory melter and drawn through orifices of platinum-alloy basedbushings to form glass fibers. Strands of glass fibers are formed bygathering the individual filaments together. The strands may be woundand further processed in a conventional manner suitable for the intendedapplication. The glass fibers of the invention are obtainable by any ofthe methods of forming glass fibers described herein.

In another embodiment of the invention, a reinforced composite productcomprising a polymer matrix and a plurality of glass fibers is provided.

In another embodiment of the present invention, glass fibers faultedfrom the inventive compositions have a liquidus temperature no greaterthan about 1320° C., a log 3 temperature less than about 1505° C., a ΔTup to about 205° C. In one embodiment, the log 3 temperature can be lessthan about 1445° C.

In another embodiment of the present invention, glass fibers formed fromthe inventive compositions have a liquidus temperature no greater thanabout 1320° C., a log 3 temperature less than about 1500° C., a ΔT up toabout 205° C.

In yet another embodiment of the invention, glass fibers formed from theinventive composition have a pristine fiber tensile strength betweenabout 4390 and about 4820 MPa, a modulus between about 82 and about 91GPa and a density between about 2.39 and 2.52 g/cc.

In yet another embodiment of the invention, glass fibers formed from theinventive composition have a pristine fiber tensile strength betweenabout 4390 and about 4820 MPa, a modulus between about 83 and about 90GPa, and a density between about 2.39 and 2.52 g/cc.

In a further embodiment of the invention, glass fibers formed from theinventive composition have a specific modulus from about 34.5 MJ/kg toabout 35.9 MJ/kg and a specific strength from about 1.8 MJ/kg to about2.0 MJ/kg.

In another embodiment of the present invention, the glass compositionpossesses a forming viscosity that is low enough, and a ΔT that is largeenough, to utilize low cost refractory melters instead of conventionalhigh cost platinum-alloy lined melters in the formation of the glassfibers.

In another embodiment of the present invention, fibers formed from theinventive composition are formed at a lower cost due to the lower energyinput needed to melt the glass composition.

The foregoing and other objects, features, and advantages of theinvention will appear more fully hereinafter from a consideration of thedetailed description that follows.

DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which the invention belongs. Although any methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of the present invention, the preferred methodsand materials are described herein. All references cited herein,including published or corresponding U.S. or foreign patentapplications, issued U.S. or foreign patents, and any other references,are each incorporated by reference in their entireties, including alldata, tables, figures, and text presented in the cited references. Theterms “composition” and “formulation” may be used interchangeablyherein. Additionally, the phrase “inventive glass composition” and“glass composition” may be interchangeably used.

The present invention relates to a glass composition used to formcontinuous glass fibers that possess an improved modulus and lowdensity. In some embodiments, the glass composition possesses a lowforming temperature and a sufficiently large ΔT to permit theutilization of low-cost refractory tank melters for the formation of theglass fibers instead of conventional high-cost paramelters formed ofplatinum. By utilizing a refractory tank formed of refractory blocks,manufacturing costs associated with the production of glass fibersproduced by the inventive composition are reduced. Additionally, theenergy necessary to melt the components of the glass composition is lessthan the energy necessary to melt many commercially available highperformance glass formulations. Such lower energy requirements may alsolower the overall manufacturing costs associated with the inventiveglass. Further, the composition of the present invention retains theability to make a commercially acceptable high performance glass fiberand fiber product produced from the glass fibers. In particular, glassfibers formed using the inventive composition may be used to formcomposite products that are both light weight and exceptionally strong.

The inventive glass composition includes the following components in theweight percent ranges given in Table 1. As used herein, the terms“weight percent” and “percent by weight” may be used interchangeably andare meant to denote the weight percent (or percent by weight) based onthe total composition.

TABLE 1 Chemical % by weight SiO₂ 60.0-73.01 Al₂O₃ 13.0-26.0  MgO 5.0-12.75 CaO 0.0-4.0  Li₂O 3.25-4.0  Na₂O 0.0-0.75

In one embodiment, the glass composition comprises SiO₂ in an amount offrom about 63.0 to about 73.0% by weight and thus includes thecomponents set forth in Table 1A.

TABLE 1A Chemical % by weight SiO₂ 60.0-73.0 Al₂O₃ 13.0-26.0 MgO 5.0-12.75 CaO 0.0-4.0 Li₂O 3.25-4.0  Na₂O  0.0-0.75

In one embodiment, the glass composition comprises SiO₂ in an amount offrom about 63.0 to about 66.0% by weight, Al₂O₃ in an amount of fromabout 21.0 to about 26.0% by weight, MgO in an amount of from 6.5 to8.5% by weight, CaO in amount of 0.0 to 2.0% by weight and Li₂O in anamount of 3.25 to 3.5% by weight, and thus includes the components setforth in Table 2.

TABLE 2 Chemical % by weight SiO₂ 63.0-66.0 Al₂O₃ 21.0-26.0 MgO 6.5-8.5CaO 0.0-2.0 Li₂O 3.25-3.5  Na₂O  0.0-0.75In this embodiment, the glass composition can comprise SiO₂ in an amountof from about 63.05 to about 65.66% by weight, Al₂O₃ in an amount offrom about 21.69 to about 26.0% by weight, MgO in an amount of from 6.88to 8.49% by weight, CaO in amount of 0.0 to 1.10% by weight, Li₂O in anamount of 3.25 to 3.41% by weight and Na₂O in amount of 0 to 0.75% byweight.

In one embodiment, the glass composition comprises MgO in an amount offrom 5.0 to 10.7% by weight, CaO in amount of 0.0 to 23% by weight andLi₂O in an amount of 3.25 to 4.0% by weight, and thus includes thecomponents set forth in Table 3.

TABLE 3 Chemical % by weight SiO₂  63.0-73.01 Al₂O₃ 13.0-26.0 MgO 5.0 to10.70 CaO 0.0-2.7 Li₂O 3.25-4.0  Na₂O  0.0-0.75In this embodiment, the glass composition can comprise MgO in an amountof from 5.0 to 10.68% by weight and CaO in amount of 0.0 to 2.66% byweight.

In another embodiment, the glass composition comprises SiO₂ in an amountof from about 60.0 to about 65.5% by weight, CaO in amount of 0.0 to2.3% by weight and Li₂O in an amount of 3.25 to 3.70% by weight, andthus includes the components set forth in Table 4.

TABLE 4 Chemical % by weight SiO₂ 60.0-65.5 Al₂O₃ 13.0-26.0 MgO 5.0-12.75 CaO 0.0-2.3 Li₂O 3.25-3.7  Na₂O  0.0-0.75

In another embodiment, the glass composition comprises SiO₂ in an amountof from about 60.0 to about 65.5% by weight, CaO in amount of 0.0 to2.3% by weight and Li₂O in an amount of 3.30 to 3.70% by weight, andthus includes the components set forth in Table 4A.

TABLE 4A Chemical % by weight SiO₂ 60.0-65.5 Al₂O₃ 13.0-26.0 MgO 5.0-12.75 CaO 0.0-2.3 Li₂O 3.30-3.7  Na₂O  0.0-0.75In this embodiment, the glass composition can comprise SiO₂ in an amountof from about 60.0 to about 65.20% by weight, Al₂O₃ in an amount of19.33 to 26.00% by weight, MgO in an amount of from 6.88 to 12.75% byweight, CaO in amount of 0.66 to 2.26% by weight, Li₂O in an amount of3.32 to 3.63% by weight and Na₂O in amount of 0.13 to 0.75% by weight.

In each of the embodiments described above, CaO can be present in anamount of at least 0.1% by weight and/or Na₂O can be present in anamount of at least 0.05% by weight.

Further, impurities or tramp materials may be present in the glasscomposition without adversely affecting the glasses or the fibers. Theseimpurities may enter the glass as raw material impurities or may beproducts formed by the chemical reaction of the molten glass withfurnace components. Non-limiting examples of tramp materials includepotassium, iron, zinc, strontium, and barium, all of which are presentin their oxide forms, and fluorine and chlorine. The glass compositionof the present invention can be free or substantially free of B₂O₃ andfluorine.

The present invention also relates to glass fibers formed from theinventive glass compositions. Pristine glass fibers (i.e., unsized anduntouched laboratory produced fibers) have a fiber tensile strengthbetween about 4390 and about 4820 MPa or between about 4500 and about4820 MPa. Additionally, the pristine fibers have a modulus between about82 and about 91 GPa or between about 83 and about 90 GPa. Additionally,the pristine fibers have a density from about 2.39 to about 2.52 g/cc.The fiber tensile strength is also referred to herein as “strength” andis measured on pristine fibers using an Instron tensile testingapparatus according to ASTM D2343-09. As referred to herein, the modulusis an average of measurements on 5 single glass fibers measured inaccordance with the procedure outlined in the report, “Glass Fiber andMeasuring Facilities at the U.S. Naval Ordnance Laboratory”, ReportNumber NOLTR 65-87, Jun. 23, 1965. The density is measured by theArchimedes method (ASTM C693-93 (2008)) on unannealed bulk glass.

In one embodiment, the glass fibers have a density of less than 2.477g/cc. In this embodiment, the glass fibers can be formed from thecomposition defined in relation to Table 3.

Fiberizing properties of the glass composition of the present inventioninclude the fiberizing temperature, the liquidus temperature, and ΔT.The fiberizing temperature is defined as the temperature thatcorresponds to a viscosity of about 1000 Poise and as used herein ismeasured using a rotating cylinder method (ASTM C965-96 (2007)). Thefiberizing temperature can also be referred to as the log 3 temperatureor the forming viscosity. Lowering the fiberizing temperature may reducethe production cost of the glass fibers because it allows for a longerbushing life and reduced energy usage. For example, at a lowerfiberizing temperature, a bushing operates at a cooler temperature anddoes not quickly “sag”. Sag is a phenomenon that occurs in bushings thatare held at an elevated temperature for extended periods of time. Thus,by lowering the fiberizing temperature, the sag rate of the bushing maybe reduced and the bushing life can be increased.

In addition, a lower fiberizing temperature allows for a higherthroughput since more glass can be melted in a given period at a givenenergy input. Additionally, a lower fiberizing temperature will permitglass formed with the inventive composition to be melted in arefractory-lined melter instead of conventional high-cost parameltersformed of platinum since both its melting and fiberizing temperaturesare below the upper use temperatures of many commercially availablerefractories. In the present invention, the glass composition has afiberizing temperature (i.e., log 3 temperature) that is less than about1505° C. and can be less than 1500° C. or less than about 1400° C. Inexemplary embodiments, the log 3 temperature is from about 1280° C. toabout 1500° C. or to about 1505° C. In one embodiment, the log 3temperature is from about 1283° C. to about 1501° C.

The liquidus temperature is defined as the highest temperature at whichequilibrium exists between liquid glass and its primary crystallinephase. As used herein the liquidus temperature is measured by exposingthe glass composition to a temperature gradient in a platinum-alloy boatfor 16 hours (ASTM C829-81 (2005)).

At all temperatures above the liquidus temperature, the glass is freefrom crystals in its primary phase. At temperatures below the liquidustemperature, crystals may form. Additionally, the liquidus temperatureis the greatest temperature at which devitrification can occur uponcooling the glass melt. At all temperatures above the liquidustemperature, the glass is completely molten. The liquidus temperature ofthe inventive composition is desirably no greater than about 1380 or1320° C., and may range from about 1230 to about 1380 or from about1250° C. to about 1320° C.

A third fiberizing property is “ΔT”, which is defined as the differencebetween the fiberizing temperature (i.e., log 3 temperature) and theliquidus temperature. If the ΔT is too small, the molten glass maycrystallize within the fiberizing apparatus and cause an interruption inthe manufacturing process. Desirably, the ΔT is as large as possible fora given forming viscosity. A larger ΔT offers a greater degree offlexibility during fiberizing and helps to avoid devitrification both inthe glass distribution system and in the fiberizing apparatus.Additionally, a large ΔT reduces the production cost of the glass fibersby allowing for a greater bushing life and a less sensitive formingprocess. The inventive composition may have a ΔT up to about 205° C.,and in exemplary embodiments, from about 28° C. to about 205° C. In oneembodiment, the inventive composition may have a ΔT up to about 50° C.

Another property of importance is the specific modulus. Is it desirableto have a specific modulus as high as possible to achieve a lightweightcomposite material that adds stiffness to the final article. Specificmodulus is important in applications where stiffness of the product isan important parameter, such as in wind energy and aerospaceapplications. In the inventive composition, the glass fibers have aspecific modulus from about 34.5 MJ/kg to about 35.9 MJ/kg. In addition,the glass fibers have a specific strength from about 1.8 MJ/kg to about2.0 MJ/kg.

In one embodiment, the glass fibers have a specific modulus of greaterthan or equal to 35.5 MJ/kg. In this embodiment, the glass fibers can beformed from the compositions defined in relation to Table 4A. In oneembodiment, the glass fibers have a specific modulus of 36.0 MJ/Kg.

In general, glass fibers according to the present invention may beformed by obtaining the raw materials or ingredients and mixing orblending the components in a conventional manner in the appropriatequantities to give the desired weight percentages of the finalcomposition. For example, the components may be obtained from suitableingredients or raw materials including, but not limited to, sand orpyrophyllite for SiO₂, limestone, burnt lime, wollastonite, or dolomitefor CaO, kaolin, alumina or pyrophyllite for Al₂O₃, dolomite, dolomiticquicklime, brucite, enstatite, talc, burnt magnesite, or magnesite forMgO, lithium carbonate or spodumene for Li₂O, and sodium carbonate,sodium feldspar, or sodium sulfate for Na₂O. Glass cullet can also beused to supply one or more of the needed oxides. The mixed batch is thenmelted in a traditional refractory furnace or melter, and the resultingmolten glass is passed along a forehearth and into bushings (e.g.,platinum-alloy based bushings) located along the bottom of theforehearth. The operating temperatures of the glass in the furnace,forehearth, and bushing are selected to appropriately adjust theviscosity of the glass, and may be maintained using suitable methodssuch as control devices. Preferably, the temperature at the front end ofthe melter is automatically controlled to reduce or eliminatedevitrification. The molten glass is then pulled (drawn) through holesor orifices in the bottom or tip plate of the bushing to form glassfibers. The streams of molten glass flowing through the bushing orificesare attenuated to filaments by winding a strand formed of a plurality ofindividual filaments on a forming tube mounted on a rotatable collet ofa winding machine or chopped at an adaptive speed.

The fibers may be further processed in a conventional manner suitablefor the intended application. For instance, the glass fibers may besized with a sizing composition known to those of skill in the art. Thesizing composition is in no way restricted, and may be any sizingcomposition suitable for application to glass fibers. The sized fibersmay be used for reinforcing substrates such as a variety of plasticswhere the product's end use requires high strength and stiffness and lowweight. Such applications include, but are not limited to, woven fabricsfor use in forming wind blades, armor plating, and aerospace structures.In this regard, the present invention also includes a composite materialincluding the inventive glass fibers, as described above, in combinationwith a hardenable matrix material. The matrix material may be anysuitable thermoplastic or thermoset resin known to those of skill in theart, such as, but not limited to thermoplastics such as polyesters,polypropylene, polyamide, polyethylene terephtalate, and polybutylene,and thermoset resins such as epoxy resins, unsaturated polyesters,phenolics, vinylesters, and elastomers. These resins can be used aloneor in combination.

Having generally described this invention, a further understanding canbe obtained by reference to certain specific examples illustrated belowwhich are provided for purposes of illustration only and are notintended to be all inclusive or limiting unless otherwise specified.

EXAMPLES Example 1 High Performance Glass Compositions

Glass compositions according to the present invention were made bymixing reagent grade chemicals in proportioned amounts to achieve afinal glass composition with the oxide weight percentages set forth inTable 4. The raw materials were melted in a platinum crucible in anelectrically heated furnace at a temperature of 1650° C. for 3 hours.The forming viscosity (i.e., the temperature that corresponds to aviscosity of about 1000 Poise) was measured using a rotating cylindermethod (ASTM C965-96 (2007)). The liquidus temperature was measured byexposing glass to a temperature gradient in a platinum-alloy boat for 16hours (ASTM C829-81 (2005)). Density was measured by the Archimedesmethod (ASTM C693-93 (2008)) on unannealed bulk glass. The modulusreported in the tables below is an average of measurements on 5 singleglass fibers measured in accordance with the procedure outlined in thereport, “Glass Fiber and Measuring Facilities at the U.S. Naval OrdnanceLaboratory”, Report Number NOLTR 65-87, Jun. 23, 1965. The strength wasmeasured on pristine filaments using an Instron tensile testingapparatus (ASTM D2343-09).

TABLE 4 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 (% by wt.) (% by wt.)(% by wt) (% by wt.) (% by wt.) (% by wt.) (% by wt.) Chemical SiO₂65.20 73.01 63.05 63.68 64.33 65.02 65.04 Al₂O₃ 21.94 16.79 26.00 19.3320.46 21.64 21.69 MgO 8.21 6.36 6.88 12.75 7.68 8.10 8.12 CaO 1.06 0.450.62 0.75 4.00 1.03 1.03 Li₂O 3.37 3.30 3.32 3.34 3.35 4.00 3.37 Na₂O0.22 0.09 0.13 0.15 0.18 0.21 0.75 Property Forming 1376 1501 1384 12941337 1356 1375 Viscosity (° C.) Liquidus 1274 1296 1317 1258 1255 12751268 Temperature (° C.) ΔT 102 205 68 35 82 81 107 (° C.) Density 2.46132.3916 2.4641 2.5026 2.4893 2.4594 2.4613 (g/cc) Modulus 87.4 82.6 88.589.6 87.1 86.5 87.5 GPa Strength 4682 4790 4735 4500 4508 4588 4688 MPaSpecific 35.5 34.5 35.9 35.8 35.0 35.2 35.5 Modulus (MJ/kg)

TABLE 5 Ex. 8 Ex. 9 Ex. 10 Ex. 11 Ex. 12 Ex. 13 (% by wt.) (% by wt.) (%by wt.) (% by wt) (% by wt.) (% by wt.) Chemical SiO₂ 60.00 69.44 66.7665.66 65.24 65.27 Al₂O₃ 23.60 13.00 22.76 22.19 21.97 21.99 MgO 10.0710.68 5.00 8.49 8.24 8.26 CaO 2.26 2.66 1.65 0.00 1.08 1.10 Li₂O 3.633.71 3.50 3.41 3.25 3.38 Na₂O 0.44 0.51 0.33 0.25 0.22 0.00 PropertyForming 1283 1302 1443 1390 1375 1376 Viscosity (° C.) Liquidus 12521273 1297 1311 1286 1297 Temperature (° C.) ΔT 31 28 146 79 89 79 (° C.)Density 2.5169 2.4704 2.4331 2.4516 2.4631 2.4622 (g/cc) Modulus 90.185.7 85.5 86.6 87.3 87.1 GPa Strength 4593 4393 4797 4691 4765 4819 MPaSpecific 35.8 34.7 35.1 35.3 35.5 35.4 Modulus (MJ/kg)

Looking at Tables 4 and 5, it can be concluded that the glasscompositions of Examples 1-13 have forming viscosity temperatures thatare applicable for use in refractory furnaces. In some cases, thespecific modulus values for the glasses nearly equal commercial S2 glassmanufactured by AGY which has a specific modulus of 36 MJ/Kg as measuredby the same method and personnel as these samples. These glasses areespecially suited for applications that require stiffness that is equalto that of S2 glass but without the high strength of S2 glass, such as,for example, wind blades. In addition, the density of some of theglasses shown in Tables 4 and 5 is extremely low, which allows theseglasses to be employed in aerospace applications. (Cf., AGY S2 at 2.477g/cc)

The invention of this application has been described above bothgenerically and with regard to specific embodiments. Although theinvention has been set forth in what is believed to be the preferredembodiments, a wide variety of alternatives known to those of skill inthe art can be selected within the generic disclosure. The invention isnot otherwise limited, except for the recitation of the claims set forthbelow.

1. A composition for preparing high strength, light weight glass fiberscomprising: SiO₂ in an amount from about 60.0 to about 73.01% by weightof the total composition, Al₂O₃ in an amount from about 13.0 to about26.0% by weight of the total composition, MgO in an amount from about5.0 to about 12.75% by weight of the total composition, CaO in an amountfrom 0.0 to about 4.0% by weight of the total composition, Li₂O in anamount from about 3.25 to about 4.0% by weight of the total composition,and Na₂O in an amount from 0.0 to about 0.75% by weight of the totalcomposition.
 2. (canceled)
 3. The glass composition of claim 1, whereinSiO₂ is present in an amount from about 63.0 to about 66.0% by weight ofthe total composition, Al₂O₃ is present in an amount from about 21.0 toabout 26.0% by weight of the total composition, MgO is present in anamount from 6.5 to about 8.5% by weight of the total composition, CaO ispresent in an amount from about 0.0 to about 2.0% by weight of the totalcomposition, and Li₂O is present in an amount from about 3.25 to about3.5% by weight of the total composition.
 4. The glass composition ofclaim 1 wherein, MgO is present in an amount from 5.0 to about 10.70% byweight of the total composition. CaO is present in an amount from about0.0 to about 2.7% by weight of the total composition, and Li₂O ispresent in an amount from about 3.25 to about 4.0% by weight of thetotal composition.
 5. The glass composition of claim 1, wherein SiO₂ ispresent in an amount from about 60.0 to about 65.5% by weight of thetotal composition, CaO is present in an amount from about 0.0 to about2.3% by weight of the total composition, and Li₂O is present in anamount from about 3.25 to about 3.7% by weight of the total composition.6. The glass composition of claim 1, wherein said composition issubstantially free of B₂O₃ and fluorine.
 7. The glass composition ofclaim 1, wherein said composition has a ΔT up to about 205° C.
 8. Theglass composition of claim 7, wherein said composition has a ΔT from 28°C. to 205° C.
 9. The glass composition of claim 1, wherein saidcomposition has a log 3 temperature from about 1280° C. to about 1505°C.
 10. The glass composition of claim 9, wherein said composition has alog 3 temperature from about 1283° C. to about 1501° C.
 11. The glasscomposition of claim 1, wherein said composition has a liquidustemperature no greater than about 1380° C.
 12. The glass composition ofclaim 11, wherein said composition has a liquidus temperature no greaterthan about 1320° C.
 13. The glass composition of claim 1, whereincomponents of said composition are melted in a refractory tank melter.14. A continuous high strength, light weight glass fiber produced from acomposition according to claim
 1. 15. The glass fiber of claim 14,wherein said glass fiber has a specific modulus from 35 MJ/kg to about36 MJ/kg and a specific strength from about 1.8 MJ/kg to about 2.0MJ/kg.
 16. The glass fiber of claim 14, wherein said glass fiber has apristine fiber tensile strength from about 4390 to about 4820 MPa, amodulus from about 82 to about 90 GPa, and a density from about 2.39 toabout 2.52 g/cc.
 17. The glass fiber of claim 16, wherein said glassfiber has a modulus between about 83 and about 90 GPa.
 18. The glassfiber of claim 16, wherein said glass fiber has a density of from 2.39to less than 2.477 g/cc.
 19. A method of forming a continuous highperformance glass fiber comprising: providing a molten glass compositionincluding a composition according to claim 1; and drawing said moltenglass composition through orifices in a bushing to form a continuousglass fiber.
 20. The method of claim 19, wherein said glass fiber has aspecific modulus from about 34.5 M J/kg to about 35.9 M J/kg and aspecific strength from about 1.8 M J/kg to about 2.0 MJ/kg.
 21. Themethod of claim 19, wherein said glass fiber has a pristine fibertensile strength from about 4390 to about 4820 MPa, a modulus from about82 to about 90 GPa, and a density from about 2.39 to about 2.52 g/cc.22. The method of claim 19, wherein said glass fiber has a modulusbetween about 83 and about 90 GPa.
 23. The method of claim 19, whereinsaid glass fiber has a density of from 2.39 to less than 2.477 g/cc. 24.A reinforced composite product comprising: a polymer matrix; and aplurality of glass fibers, wherein said glass fibers are according toclaim
 14. 25. The composite product of claim 24, wherein said polymermatrix is a thermoplastic polymer selected from polyesters,polypropylene, polyamide, polyethylene terephtalate, polybutylene andcombinations thereof.
 26. The composite product of claim 24, whereinsaid polymer matrix is a thermoset polymer selected from epoxy resins,unsaturated polyesters, phenolics, vinylesters and combinations thereof.27. A method of preparing a reinforced composite product comprisingpreparing a plurality of fibers according to the method of claim 19 andcombining said fibers with at least one polymer matrix material. 28-30.(canceled)